Curable coating composition

ABSTRACT

A curable coating composition is described comprising 
     (A) a carbamate- or urea-functional compound that is the reaction product of 
     (1) a compound comprising a carbamate or urea group or a group that can be converted to carbamate or urea, and a hydroxyl functional group that is the reaction product of 
     (a) a compound comprising a carbamate or urea group or a group that can be converted to a carbamate or urea group, and an active hydrogen group that is reactive with a lactone or a hydroxy carboxylic acid, and 
     (b) a lactone or hydroxy carboxylic acid, and 
     (2) a component that is reactive with compound (A)(1) to convert a hydroxyl group on compound (A)(1) to a carbamate group, or a component comprising a group that is reactive with a hydroxyl group on compound (A)(1) and a carbamate or urea group or group that can be converted to carbamate or urea, 
     (B) a compound comprising a plurality of groups that are reactive with carbamate or urea.

This is a continuation of U.S. Ser. No. 08/540,277 filed Oct. 6, 1995,now abandoned.

FIELD OF THE INVENTION

This invention relates to curable coating compositions, particularly tocurable compositions utilizing a carbamate- or urea-functional compoundas one of the components of the composition.

BACKGROUND OF THE INVENTION

Curable coating compositions such as thermoset coatings are widely usedin the coatings art. They are often used for topcoats in the automotiveand industrial coatings industry. Color-plus-clear composite coatingsare particularly useful as topcoats where exceptional gloss, depth ofcolor, distinctness of image, or special metallic effects are desired.The automotive industry has made extensive use of these coatings forautomotive body panels. Color-plus-clear composite coatings, however,require an extremely high degree of clarity in the clearcoat to achievethe desired visual effect. High-gloss coatings also require a low degreeof visual aberations at the surface of the coating in order to achievethe desired visual effect such as high distinctness of image (DOI).

Such coatings are especially susceptible to a phenomenon known asenvironmental etch. Environmental etch manifests itself as spots ormarks on or in the finish of the coating that often cannot be rubbedout.

Curable coating compositions based on curable components havingcarbamate or urea functionality have been proposed have been describedin the art to provide etch-resistant coatings, e.g., U.S. Pat. No.5,356,669 and WO 94/10211.

In addition to resistance to environmental etch, a number of othercharacteristics can be desirable. For example, it may be desirable toprovide a coating having a high degree of flexibility. This can beparticularly advantageous if the substrate on which the coating isplaced is itself flexible, as in the case of plastic, leather, ortextile substrates.

It is also desirable to reduce the amount of solvent required in coatingcompositions in order to reduce the volatile organic content (VOC),which is better for the environment.

Finally, it is desirable to provide options of different types ofcarbamate- or urea-functional materials to provide coatings with a goodcombination of properties such as durability, hardness, and resistanceto scratching, marring, solvents, and acids.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a coatingcomposition comprising

(A) a carbamate- or urea-functional compound that is the reactionproduct of

(1) a compound comprising a carbamate or urea group or a group that canbe converted to carbamate or urea, and a hydroxyl functional group thatis the reaction product of

(a) a compound comprising a carbamate or urea group or a group that canbe converted to a carbamate or urea group, and an active hydrogen groupthat is reactive with a lactone or a hydroxy carboxylic acid, and

(b) a lactone or a hydroxy carboxylic acid, and

(2) a component that is reactive with compound (A)(1) to convert ahydroxyl group on compound (A)(1) to a carbamate group, or a componentcomprising a group that is reactive with a hydroxyl group on compound(A)(1) and a carbamate or urea group or group that can be converted tocarbamate or urea,

(B) a compound comprising a plurality of groups that are reactive withcarbamate or urea.

The present invention provides coatings having a good combination ofproperties such as durability, hardness, and resistance to scratching,marring, solvents, and acids. Coating compositions according to theinvention can also provide low VOC levels, and can be used to preparecoatings having good flexibility for use over flexible substrates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, compound (A) has carbamate or ureafunctionality, and is formed by reaction of a compound (A)(1) havingcarbamate or urea groups or groups that can be converted to carbamate orurea and hydroxyl groups, with a compound (A)(2). Compound (A)(1) is thereaction product of a compound having at least one carbamate or ureagroup (or a group that can be converted to carbamate or urea) and anactive hydrogen group (A)(1)(a) with a lactone or hydroxy carboxylicacid (A)(1)(b).

Carbamate groups can generally be characterized by the formula ##STR1##wherein R is H or alkyl, preferably of 1 to 4 carbon atoms. Preferably,R is H or methyl, and more preferably R is H. Urea groups can generallybe characterized by the formula ##STR2## wherein R' and R" eachindependently represents H or alkyl, preferably of 1 to 4 carbon atoms,or R' and R" may together form a heterocyclic ring structure (e.g.,where R' and R" form an ethylene bridge).

The compound (A)(1) can be formed by reacting a lactone or hydroxycarboxylic acid with a compound having an active hydrogen group capableof ring-opening the lactone (e.g., hydroxyl, primary amine, acid) orundergoing a condensation reaction with the hydroxy carboxylic acid anda carbamate or urea group or a group that can be converted to carbamateor urea. When a compound having an active hydrogen group and a groupthat can be converted to carbamate or urea is used to react with thelactone or hydroxy carboxylic acid, conversion of the group to acarbamate or urea can be accomplished during or after the ring-openingreaction.

Compounds having a carbamate or urea group and an active hydrogen groupare known in the art. Hydroxypropyl carbamate and hydroxyethyl ethyleneurea, for example, are well known and commercially available. Aminocarbamates are described in U.S. Pat. No. 2,842,523. Hydroxyl ureas mayalso be prepared by reacting an oxazolidone with ammonia or a primaryamine or by reacting ethylene oxide with ammonia to form an aminoalcohol and then reacting the amine group of that compound or any otheramino alcohol with hydrochloric acid, then urea to form a hydroxy urea.Amino ureas can be prepared, for example, by reacting a ketone with adiamine having one amine group protected from reaction (e.g., by sterichindrance), followed by reaction with HNCO (i.e., the product of thethermal decomposition of urea), and then water. Alternatively, thesecompounds can be prepared by starting with a compound having an activehydrogen and a group that can be converted to carbamate or urea asdescribed below, and then converting that group to the carbamate or ureaprior to commencement of the reaction with the lactone or hydroxycarboxylic acid.

Groups that can be converted to carbamate include cyclic carbonategroups, epoxy groups, and unsaturated bonds. Cyclic carbonate groups canbe converted to carbamate groups by reaction with ammonia or a primaryamine, which ring-opens the cyclic carbonate to form a β-hydroxycarbamate. Epoxy groups can be converted to carbamate groups by firstconverting to a cyclic carbonate group by reaction with CO₂. This can bedone at any pressure from atmospheric up to supercritical CO₂ pressures,but is preferably under elevated pressure (e.g., 60-150 psi). Thetemperature for this reaction is preferably 60°-150° C. Useful catalystsinclude any that activate an oxirane ring, such as tertiary amine orquaternary salts (e.g., tetramethyl ammonium bromide), combinations ofcomplex organotin halides and alkyl phosphonium halides (e.g., (CH₃)₃SnI, Bu₄ SnI, Bu₄ PI, and (CH₃)₄ PI), potassium salts (e.g., K₂ CO₃, KI)preferably in combination with crown ethers, tin octoate, calciumoctoate, and the like. The cyclic carbonate group can then be convertedto a carbamate group as described above. Any unsaturated bond can beconverted to carbamate groups by first reacting with peroxide to convertto an epoxy group, then with CO₂ to form a cyclic carbonate, and thenwith ammonia or a primary amine to form the carbamate.

Other groups, such as hydroxyl groups or isocyanate groups can also beconverted to carbamate groups to form a compound (A)(1)(a). However, ifsuch groups were to be present on the compound (A)(1)(a) and thenconverted to carbamate after reaction with the lactone or hydroxycarboxylic acid, they would have to be blocked so that they would notreact with the lactone, the hydroxy carboxylic acid, or with otheractive hydrogen groups. When blocking these groups is not feasible, theconversion to carbamate or urea would have to be completed prior to thereaction with the lactone or hydroxy carboxylic acid. Hydroxyl groupscan be converted to carbamate groups by reaction with a monoisocyanate(e.g., methyl isocyanate) to form a secondary carbamate group or withcyanic acid (which may be formed in situ by thermal decomposition ofurea) to form a primary carbamate group (i.e., unsubstitutedcarbamates). This reaction preferably occurs in the presence of acatalyst as is known in the art. A hydroxyl group can also be reactedwith phosgene and then ammonia to form a compound having primarycarbamate group(s), or by reaction of a hydroxyl with phosgene and thena primary amine to form a compound having secondary carbamate groups.Another approach is to react an isocyanate with a compound such ashydroxyalkyl carbamate to form a carbamate-capped isocyanate derivative.For example, one isocyanate group on toluene diisocyanate can be reactedwith hydroxypropyl carbamate, followed by reaction of the otherisocyanate group with an excess of polyol to form a hydroxy carbamate.Finally, carbamates can be prepared by a transesterification approachwhere hydroxyl group reacted with an alkyl carbamate (e.g., methylcarbamate, ethyl carbamate, butyl carbamate) to form a primary carbamategroup-containing compound. This reaction is performed under heat,preferably in the presence of a catalyst such as an organometalliccatalyst (e.g., dibutyltin dilaurate). Other techniques for preparingcarbamates are also known in the art and are described, for example, inP. Adams & F. Baron, "Esters of Carbamic Acid", Chemical Review, v. 65,1965.

Groups such as oxazolidone can also be converted to urea after reactionwith the lactone or hydroxy carboxylic acid. For example, hydroxyethyloxazolidone can be used to initiate the reaction with the lactone orhydroxy carboxylic acid, followed by reaction of ammonia or a primaryamine with the oxazolidone to generate the urea functional group.

Other groups, such as amino groups or isocyanate groups can also beconverted to urea groups to form a compound (A)(1)(a). However, if suchgroups were to be present on the compound (A)(1)(a) and then convertedto urea after the reaction with the lactone or hydroxy carboxylic acid,they would have to be blocked so that they would not react with thelactone, the hydroxy carboxylic acid, or with other active hydrogengroups. When blocking these groups is not feasible, the conversion tocarbamate or urea would have to be completed prior to the reaction withthe lactone or hydroxy carboxylic acid. Amino groups can be converted tourea groups by reaction with a monoisocyanate (e.g., methyl isocyanate)to form a secondary urea group or with cyanic acid (which may be formedin situ by thermal decomposition of urea) to form a primary urea group.This reaction preferably occurs in the presence of a catalyst as isknown in the art. An amino group can also be reacted with phosgene andthen ammonia to form a compound having primary urea group(s), or byreaction of an amino group with phosgene and then a primary amine toform a compound having secondary urea groups. Another approach is toreact an isocyanate with a hydroxy urea compound to form a urea-cappedisocyanate derivative. For example, one isocyanate group on toluenediisocyanate can be reacted with hydroxyethyl ethylene urea, followed byreaction of the other isocyanate group with an excess of polyol to forma hydroxy carbamate.

One preferred class of compounds having an active hydrogen group and agroup that can be converted to carbamate is the hydroxyalkyl cycliccarbonates. Hydroxyalkyl cyclic carbonates can be prepared by a numberof approaches. Certain hydroxyalkyl cyclic carbonates like3-hydroxypropyl carbonate (i.e., glycerine carbonate) are commerciallyavailable. Cyclic carbonate compounds can be synthesized by any ofseveral different approaches. One approach involves reacting an epoxygroup-containing compound with CO₂, under conditions and with catalystsas described hereinabove. Epoxides can also be reacted withβ-butyrolactone in the presence of such catalysts. In another approach,a glycol like glycerine is reacted at temperatures of at least 80° C.with diethyl carbonate in the presence of a catalyst (e.g., potassiumcarbonate) to form a hydroxyalkyl carbonate. Alternatively, a functionalcompound containing a ketal of a 1,2-diol having the structure: ##STR3##can be ring-opened with water, preferably with a trace amount of acid,to form a 1,2-glycol, which is then further reacted with diethylcarbonate to form the cyclic carbonate.

Cyclic carbonates typically have 5-6-membered rings, as is known in theart. Five-membered rings are preferred, due to their ease of synthesisand greater degree of commercial availability. Six-membered rings can besynthesized by reacting phosgene with 1,3-propane diol under conditionsknown in the art for the formation of cyclic carbonates. Preferredhydroxyalkyl cyclic carbonates used in the practice can be representedby the formula: ##STR4## where R (or each instance of R if n is morethan 1) is a hydroxyalkyl group of 1-18 carbon atoms, preferably 1-6carbon atoms, and more preferably 1-3 carbon atoms, which may be linearor branched and may have subsituents in addition to the hydroxyl (whichitself may be primary, secondary, or tertiary), and n is 1 or 2, whichmay be substituted by one or more other substituents such as blockedamines or unsaturated groups. More preferably, R is --C_(m) H_(2m) OHwhere the hydroxyl may be primary or secondary and m is 1 to 8, and evenmore preferably, R is --(CH₂)_(p) --OH where the hydroxyl is primary andp is 1 to 2.

Lactones that can be ring opened by an active hydrogen are well-known inthe art. They include, for example, ε-caprolactone, γ-caprolactone,β-butyrolactone, β-propriolactone, γ-butyrolactone,α-methyl-γ-butyrolactone, β-methyl-γ-butyrolactone, γ-valerolactone,δ-valerolactone, γ-nonanoic lactone, γ-octanoic lactone, andpentolactone. In one preferred embodiment, the lactone isε-caprolactone. Lactones useful in the practice of the invention canalso be characterized by the formula: ##STR5## wherein n is a positiveinteger of 1 to 7 and R is one or more H atoms, or substituted orunsubstituted alkyl groups of 1-7 carbon atoms.

The lactone ring-opening reaction is typically conducted under elevatedtemperature (e.g., 80°-150° C.). The reactants are usually liquids so asolvent is not necessary. However, a solvent may be useful in promotinggood conditions for the reaction even if the reactants are liquid. Anynon-reactive solvent may be used, including both polar and nonpolarorganic solvents. Examples of useful solvents include toluene, xylene,methyl ethyl ketone, methyl isobutyl ketone, and the like. A catalyst ispreferably present. Useful catalysts include proton acids (e.g.,octanoic acid, Amberlyst® 15 (Rohm & Haas)), and tin catalysts (e.g.,stannous octoate). Alternatively, the reaction can be initiated byforming a sodium salt of the hydroxyl group on the molecules to reactwith the lactone ring.

The lactone ring-opening reaction provides chain extension of themolecule if sufficient amounts of the lactone are present. The relativeamounts of the carbamate or urea compound (A)(1)(a) and the lactone(A)(1)(b) can be varied to control the degree of chain extension. Theopening of the lactone ring with a hydroxyl or amine group results inthe formation of an ester or amide and an OH group. The OH group canthen react with another available lactone ring, thus resulting in chainextension. The reaction is thus controlled by the proportion of lactonein the relative to the amount of initiator compound (A)(1)(a). In thepractice of the present invention, the ratio of equivalents of lactonefrom (A)(1)(b) to equivalents of active hydrogen groups on (A)(1)(a) ispreferably from 0.1:1 to 10:1, and more preferably from 1:1 to 5:1. Whenthe lactone is opened with with an acid, the resulting compound has anacid group, which can then be converted to a hydroxyl group bywell-known techniques such as reaction with ethylene oxide.

A compound (A)(1) having a hydroxyl active hydrogen group can also bereacted with a hydroxy carboxylic acid to form the carbamate- orurea-functional compound (A). Useful hydroxy carboxylic acids includedimethylhydroxypropionic acid, hydroxy stearic acid, tartaric acid,lactic acid, 2-hydroxyethyl benzoic acid, and N-(2-hydroxyethyl)ethylenediamine triacetic acid. The reaction can be conducted under typicaltransesterification conditions, e.g., temperatures from room temperatureto 150° C. with transesterification catalysts such as such as calciumoctoate, metal hydroxides (e.g., KOH), Group I or II metals (e.g., Na,Li), metal carbonates (e.g., K₂ CO₃) which may be enhanced by use incombination with crown ethers, metal oxides (e.g., dibutyltin oxide),metal alkoxides (e.g., NaOCH₃, Al(OC₃ H₇)₃), metal esters (e.g.,stannous octoate, calcium octoate, or protic acids (e.g., H₂ SO₄),MgCO₃, or Ph₄ SbI. The reaction may also be conducted at roomtemperature with a polymer-supported catalyst such as Amberlyst-15®(Rohm & Haas) as described by R. Anand, Synthetic Communications,24(19), 2743-47 (1994), the disclosure of which is incorporated hereinby reference.

The terminal hydroxyl group on compound (A)(1) is then converted tocarbamate or urea by reaction with a compound (A)(2), which is reactivewith compound (A)(1) to convert a hydroxyl group on compound (A)(1) to acarbamate or urea group, or which comprises a group that is reactivewith a hydroxyl group on compound (A)(1) and a carbamate or urea groupor group that can be converted to carbamate or urea.

A number of compounds may be used as compound (A)(2) to convert ahydroxyl group on compound (A)(1) to a carbamate group. Hydroxyl groupscan be converted to carbamate groups by reaction with a monoisocyanate(e.g., methyl isocyanate) to form a secondary carbamate group or withcyanic acid (which may be formed by the thermal decomposition of urea)to form a primary carbamate group (i.e., unsubstituted carbamates). Thisreaction is performed preferably in the presence of a catalyst as isknown in the art. A hydroxyl group can also be reacted with phosgene andthen ammonia to form a compound having primary carbamate group(s), or byreaction of a hydroxyl with phosgene and then a primary amine to form acompound having secondary carbamate groups.

Various compounds can be used as compound (A)(2) that have a group thatis reactive with the hydroxyl group on (A)(1) and a carbamate or ureagroup or a group that can be converted to carbamate or urea. Alkylcarbamates (e.g., methyl carbamate, butyl carbamate) or substitutedalkyl carbamates (e.g., hydroxypropyl carbamate) can be transesterifiedwith the hydroxyl group on compound (A)(1). This reaction is performedunder heat, preferably in the presence of a catalyst such as anorganometallic catalyst (e.g., dibutyltin dilaurate). A methylolacrylamide can be reacted with the hydroxyl group on (A)(1) and thenconverted to carbamate. In this reaction, the unsaturated bond is thenreacted with peroxide, CO₂, and ammonia as described above.Partially-blocked toluene diisocyanate can also be used as compound(A)(2). In one embodiment, the unblocked isocyanate on thepartially-blocked toluene diisocyanate can be reacted with the hydroxylgroup on (A)(1). The other isocyanate can then be unblocked and reactedwith a hydroxyalkyl carbamate (e.g., hydroxypropyl carbamate) or ahydroxy urea (e.g., hydroxyethyl ethylene urea). Alternatively, theunblocked isocyanate can be reacted with a hydroxyalkyl carbamate (e.g.,hydroxypropyl carbamate) or a hydroxy urea (e.g., hydroxyethyl ethyleneurea), followed by unblocking of the other isocyanate group and reactionwith the hydroxyl group on compound (A)(1). Other polyisocyanates can beused to append carbamate or urea groups onto the hydroxyl group on(A)(1), but they will result in competing side reactions where thepolyisocyanate reacts with more than one (A)(1) molecule or more thanone hydroxyalkyl carbamate or hydroxy urea.

The composition of the invention is cured by a reaction of thecarbamate- or urea-functional compound (A) with a component (B) that isa compound having a plurality of functional groups that are reactivewith the carbamate or urea groups on component (A). Such reactive groupsinclude active methylol or methylalkoxy groups on aminoplastcrosslinking agents or on other compounds such as phenol/formaldehydeadducts, siloxane or silane groups, and anhydride groups. Examples of(B) compounds include melamine formaldehyde resin (including monomericor polymeric melamine resin and partially or fully alkylated melamineresin), urea resins (e.g., methylol ureas such as urea formaldehyderesin, alkoxy ureas such as butylated urea formaldehyde resin),N-methylol acrylamide emulsions, isobutoxy methyl acrylamide emulsions,polyanhydrides (e.g., polysuccinic anhydride), and siloxanes or silanes(e.g., dimethyldimethoxy silane). Aminoplast resin such as melamineformaldehyde resin or urea formaldehyde resin are especially preferred.Also preferred are aminoplast resins where one or more of the aminonitrogens is substituted with a carbamate group for use in a processwith a curing temperature below 150° C., as described in U.S. Pat. No.5,300,328.

A solvent may optionally be utilized in the coating composition used inthe practice of the present invention. The coating composition accordingto the present invention can be applied without solvent, especially ifthe degree of chain extension for component (A) is limited. However, inmany cases, it is desirable to use a solvent in the coating compositionas well. This solvent should act as a solvent with respect to both thecarbamate- or urea-functional compound (A) as well as the component (B).In general, depending on the solubility characteristics of components(A) and (B), the solvent can be any organic solvent and/or water. In onepreferred embodiment, the solvent is a polar organic solvent. Morepreferably, the solvent is a polar aliphatic solvents or polar aromaticsolvents. Still more preferably, the solvent is a ketone, ester,acetate, aprotic amide, aprotic sulfoxide, or aprotic amine. Examples ofuseful solvents include methyl ethyl ketone, methyl isobutyl ketone,amyl acetate, ethylene glycol butyl ether-acetate, propylene glycolmonomethyl ether acetate, xylene, N-methylpyrrolidone, or blends ofaromatic hydrocarbons. In another embodiment, the solvent can be wateror a mixture of water with co-solvents.

The coating composition used in the practice of the invention mayinclude a catalyst to enhance the cure reaction. For example, whenaminoplast compounds, especially monomeric melamines, are used ascomponent (B), a strong acid catalyst may be utilized to enhance thecure reaction. Such catalysts are well-known in the art and include, forexample, p-toluenesulfonic acid, dinonylnaphthalene disulfonic acid,dodecylbenzenesulfonic acid, phenyl acid phosphate, monobutyl maleate,butyl phosphate, and hydroxy phosphate ester. Other catalysts that maybe useful in the composition of the invention include Lewis acids, zincsalts, and tin salts.

Although a solvent may be present in the coating composition in anamount of from about 0.01 weight percent to about 99 weight percent, itis preferably present in an amount of less than 35%, more preferablyless than 25% and most preferably less than 15%. The coating compositionpreferably has a VOC (VOC is defined herein as VOC according to ASTMD3960) of less than 3.5 lbs/gal, more preferably less than 2.5 lbs/gal,and most preferably less than 1.5 lbs/gal.

Coating compositions can be coated on the article by any of a number oftechniques well-known in the art. These include, for example, spraycoating, dip coating, roll coating, curtain coating, and the like. Forautomotive body panels, spray coating is preferred. One advantage thatcan be achieved with coating compositions according to the invention isthat coatings with a high degree of flexibility can be prepared.Accordingly, in a preferred embodiment, the substrate onto which thecoating is applied is flexible, such as plastic, leather, or textilesubstrates.

Any additional agent used, for example, surfactants, fillers,stabilizers, wetting agents, dispersing agents, adhesion promoters, UVabsorbers, HALS, etc. may be incorporated into the coating composition.While the agents are well-known in the prior art, the amount used mustbe controlled to avoid adversely affecting the coating characteristics.

In one preferred embodiment, the coating composition according to theinvention is preferably utilized in a high-gloss coating and/or as theclearcoat of a composite color-plus-clear coating. High-gloss coatingsas used herein are coatings having a 20° gloss (ASTM D523-89) or a DOI(ASTM E430-91) of at least 80. In other preferred embodiments, thecoating composition may be utilized to prepare high-gloss or low-glossprimer or enamel coatings.

When the coating composition of the invention is used as a high-glosspigmented paint coating, the pigment may be any organic or inorganiccompounds or colored materials, fillers, metallic or other inorganicflake materials such as mica or aluminum flake, and other materials ofkind that the art normally names as pigments. Pigments are usually usedin the composition in an amount of 2% to 350%, based on the total weight(not including solvent) of components A and B (i.e., a P:B ratio of 0.02to 3.5).

When the coating composition according to the invention is used as theclearcoat of a composite color-plus-clear coating, the pigmentedbasecoat composition may any of a number of types well-known in the art,and does not require explanation in detail herein. Polymers known in theart to be useful in basecoat compositions include acrylics, vinyls,polyurethanes, polycarbonates, polyesters, alkyds, and siloxanes.Preferred polymers include acrylics and polyurethanes. In one preferredembodiment of the invention, the basecoat composition also utilizes acarbamate-functional acrylic polymer. Basecoat polymers are preferablycrosslinkable, and thus comprise one or more type of cross-linkablefunctional groups. Such groups include, for example, hydroxy,isocyanate, amine, epoxy, acrylate, vinyl, silane, and acetoacetategroups. These groups may be masked or blocked in such a way so that theyare unblocked and available for the cross-linking reaction under thedesired curing conditions, generally elevated temperatures. Usefulcross-linkable functional groups include hydroxy, epoxy, acid,anhydride, silane, and acetoacetate groups. Preferred cross- linkablefunctional groups include hydroxy functional groups and amino functionalgroups.

Basecoat polymers may be self-cross-linkable, or may require a separatecross-linking agent that is reactive with the functional groups of thepolymer. When the polymer comprises hydroxy functional groups, forexample, the cross-linking agent may be an aminoplast resin, isocyanateand blocked isocyanates (including isocyanurates), and acid or anhydridefunctional cross-linking agents.

The coating compositions described herein are preferably subjected toconditions so as to cure the coating layers. Although various methods ofcuring may be used, heat-curing is preferred. Generally, heat curing iseffected by exposing the coated article to elevated temperaturesprovided primarily by radiative heat sources. Curing temperatures willvary depending on the particular blocking groups used in thecross-linking agents, however they generally range between 93° C. and177° C. The coating composition according to the present invention iscurable even at relatively low cure temperatures. Thus, in a preferredembodiment, the cure temperature is preferably between 115° C. and 150°C., and more preferably at temperatures between 115° C. and 138° C. fora blocked acid catalyzed system. For an unblocked acid catalyzed system,the cure temperature is preferably between 82° C. and 99° C. The curingtime will vary depending on the particular components used, and physicalparameters such as the thickness of the layers, however, typical curingtimes range from 15 to 60 minutes, and preferably 15-25 minutes forblocked acid catalyzed systems and 10-20 minutes for unblocked acidcatalyzed systems.

The invention is further described in the following examples.

Preparation 1

In a three necked three liter flask equipped with an agitator,thermocouple, nitrogen line, and condenser, were added 841.5 ghydroxypropyl carbamate, 806.9 g ε-caprolactone, and 2.8 g stannousoctoate under nitrgen atmosphere. The mixture was heated to atemperature of 130° C. for a period of 5.5 hours and then cooled to roomtemperature.

Preparation 2

To 200 parts of Preparation 1 was added 102.7 parts of urea, and 1.6parts of diethylene triamine. The system was heated to 130° C. and heldfor 1 hour. The system was then heated to 140° C. for 5.5 hours. Thisresulted in the formation of cyanic acid from the thermal decompositionof the urea, which reacted with the hydroxyl groups on the Preparation 1compound form carbamate groups. The resulting solid product was washedwith ethyl acetate, disolved in methylene chloride, and filtered. Themethylene chloride was then removed by evaporation to yield the finalproduct.

EXAMPLE 1

The following components were mixed and drawn down on glass substrate toform an 8 mm-thick layer:

6.2 g Preparation 2

1.7 g Resimene® 747 melamine resin

0.04 g dodecylbenzene sulfonic acid

10 g amyl acetate

The coated glass substrate was baked at 250° F. for 30 minutes,resulting in a clear tack-free film that passed 200 methylethyl ketonedouble rubs with only surface scratches.

The invention has been described in detail with reference to preferredembodiments thereof. It should be understood, however, that variationsand modifications can be made within the spirit and scope of theinvention.

What is claimed is:
 1. A curable coating composition comprising(A) thereaction product of (1) a compound comprising carbamate or urea andhydroxyl functional groups that is the reaction product of(a) a compoundcomprising a carbamate or urea group or a group that can be converted toa carbamate or urea group, and an active hydrogen group that is reactivewith a lactone or hydroxy carboxylic acid, and (b) a lactone or hydroxycarboxylic acid, and (2) a component that is reactive with compound(A)(1) to convert a hydroxyl group on compound (A)(1) to a carbamategroup, or a component comprising a group that is reactive with ahydroxyl group on compound (A)(1) and a carbamate or urea group or groupthat can be converted to carbamate or urea, wherein the carbamate grouphas a formula ##STR6## wherein R is H or alkyl; and further wherein theurea group has a formula ##STR7## wherein R' and R" each independentlyare H or alkyl, or R' and R" together form a heterocyclic ringstructure; and(B) a compound comprising a plurality of groups that arereactive with carbamate or urea.
 2. A coating composition according toclaim 1 wherein said compound (A)(1) comprises a carbamate group.
 3. Acoating composition according to claim 1 wherein said compound (A)(1)comprises a urea group.
 4. A coating composition according to claim 1wherein said active hydrogen group on compound (A)(1)(a) is a hydroxylgroup.
 5. A coating composition according to claim 1 wherein said activehydrogen group on compound (A)(1)(a) is an amino group.
 6. A coatingcomposition according to claim 1 wherein said compound (A)(1)(a) is ahydroxyalkyl carbamate or hydroxyalkyl cyclic carbonate.
 7. A coatingcomposition according to claim 1 wherein compound (A)(1)(a) is aβ-hydroxy carbamate that is a product of a ring-opened cyclic carbonate.8. A coating composition according to claim 1 wherein (A)(1)(b) is alactone.
 9. A coating composition according to claim 1 wherein the ratioof equivalents of lactone from (A)(1)(b) to equivalents of activehydrogen groups on (A)(1)(a) is from 0.1:1 to 10:1.
 10. A coatingcomposition according to claim 1 wherein the ratio of equivalents oflactone from (A)(1)(b) to equivalents of active hydrogen groups on(A)(1)(a) is from 1:1 to 5:1.
 11. A coating composition according toclaim 1 wherein compound (B) is an aminoplast.
 12. A coating compositionaccording to claim 11 wherein said aminoplast is a melamine resin.
 13. Acoating composition according to claim 1 having a VOC of less than 3.5lbs/gal.
 14. A coating composition according to claim 1 having a VOC ofless than 2.5 lbs/gal.
 15. A coating composition according to claim 1having a VOC of less than 1.5 lbs/gal.
 16. A coating compositionaccording to claim 1 that is a liquid and comprises less than 35 weightpercent of nonreactive organic solvent.
 17. A coating compositionaccording to claim 16 that is a liquid and comprises less than 25 weightpercent of nonreactive organic solvent.
 18. A coating compositionaccording to claim 16 that is a liquid and comprises less than 15 weightpercent of nonreactive organic solvent.
 19. A coating compositionaccording to claim 1 that is a clear coating composition.
 20. A coatingcomposition according to claim 1, further comprising a pigment.
 21. Acoating composition according to claim 1 wherein said component (A)(2)is a component to convert a hydroxyl group on compound (A)(1) to acarbamate or urea.
 22. A coating composition according to claim 21wherein said component (A)(2) is an alkyl carbamate or hydroxyalkylcarbamate.
 23. A coating composition according to claim 21 wherein saidcomponent (A)(2) is the thermal decomposition by-product of urea.
 24. Acoating composition according to claim 21 wherein said component (A)(2)comprises phosgene and ammonia.
 25. A coating composition according toclaim 1 wherein said component (A)(2) is a component comprising a groupthat is reactive with a hydroxyl group on compound (A)(1) and acarbamate or urea group or a group that can be converted to carbamate orurea.
 26. A method of preparing a curable coating composition,comprising the steps of:(a) reacting together (i) a compound comprisinga carbamate or urea group or a group that can be converted to acarbamate or urea group, and an active hydrogen group that is reactivewith a lactone or hydroxy carboxylic acid, and (ii) a lactone or hydroxycarboxylic acid to form a first compound comprising carbamate or ureaand hydroxyl functional groups;(b) reacting the first compound with acomponent that is reactive with the first compound to convert a hydroxylgroup on the first compound to a carbamate group, or a componentcomprising a group that is reactive with a hydroxyl group on the firstcompound and a carbamate or urea group or group that can be converted tocarbamate or urea, wherein the carbamate group has a formula ##STR8##wherein R is H or alkyl; and further wherein the urea group has aformula ##STR9## wherein R' and R" each independently are H or alkyl, orR' and R" together form a heterocyclic ring structure; and(c) combiningthe reaction product of step (b) with a compound comprising a pluralityof groups that are reactive with carbamate or urea.